I've been reading up lately on how fiat money systems work, and it doesn't seem to me that boots and guns really help. Certainly there have been countries with plenty of soldiers who failed to maintain the value of their currency.

You have to pay taxes in the local currency, but if the currency crashes you just have to pay a higher nominal amount of taxes.

You can outlaw competing currencies, but you can only do that in your own country, and it doesn't necessarily keep your official currency from going down the toilet.

It can help. I'd argue that the US-Saudi deal [1] was in part facilitated by the US being able to offer the Saudi regime military supplies and protection. The military is arguably not the dominant factor, but that is a very debatable point. It is certainly a factor.

[1] https://www.bloomberg.com/news/features/2016-05-30/the-untol...

Fiat currency is essentially the government's IOUs denominated in themselves e.g. holding a dollar note entitles you to one dollar from the government.

It only has value because a government can ask others to settle part of this debt or take their property otherwise. Naturally, the amount of debt a government can issue this way is limited by the value of property it can threaten.

Zimbabwe, for example, cannot reach much of valuable property despite having some guns and boots. But the USA is a very different matter.

The US' military might is the only reason why all oil is traded in USD and the main reason why the USD holds value.

Ok but what about all the other fiat currencies of the world?